This is one area where I disagree with my hippie friends: Human childbirth *should* be medicalized, because it's so fraught with danger (due to our skull size and bipedalism, with extra risk of infection, etc.). Perinatal mortality was high in the Western world until recently, too -- a fact that becomes sadly and personally apparent when doing genealogy. Wenda Trevathan has written some interesting stuff about human childbirth that's worth looking at: http://www.amazon.com/Ancient-Bodies-Modern-Lives-Evolution/dp/0195388887/ref=ntt_at_ep_dpt_3

Good question. As far as I know this was always the tricky bit about primitive societies, and why people always throw that shorter lifespan statistic at us. You've piqued my interest though, and I'll have to get researching.

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"Newborns are particularly susceptible to shortfalls in caloric intake. They are dependent on their mother???s milk for calories. I know the agricultural diet is nutritionally deficient, I???m not gonna argue that it is. The farmers??? diet has made us less robust and susceptible to dietary diseases. But it is rich in calories and the greater accessibility to calories that come with agriculture improves likelihood of young children reaching sexual maturity."

I think the hard thing to figure out here is if hunter-gatherer's were always as food insecure as they are today. If hunting was generally good, and nutrition somewhat stable, I'd think the infant mortality rate would be much lower.